Nginx: Beginner’s Guide

This guide gives a basic introduction to nginx and describes some simple tasks that can be done with it. It is supposed that nginx is already installed on the reader’s machine. If it is not, see the Installing
nginx page. This guide describes how to start and stop nginx, and reload its configuration, explains the structure of the configuration file and describes how to set up nginx to serve out static content, how to configure nginx as a proxy server, and how
to connect it with a FastCGI application.

nginx has one master process and several worker processes. The main purpose of the master process is to read and evaluate configuration, and maintain worker processes. Worker processes do actual processing of requests. nginx employs event-based model and OS-dependent
mechanisms to efficiently distribute requests among worker processes. The number of worker processes is defined in the configuration file and may be fixed for a given configuration or automatically adjusted to the number of available CPU cores (seeworker_processes).

The way nginx and its modules work is determined in the configuration file. By default, the configuration file is named

nginx.conf

and placed in the directory

/usr/local/nginx/conf

,

/etc/nginx

, or

/usr/local/etc/nginx

.

Starting, Stopping, and Reloading Configuration

To start nginx, run the executable file. Once nginx is started, it can be controlled by invoking the executable with the

-s

parameter. Use the following syntax:

nginx -s signal

Where signal may be one of the following:

stop

— fast shutdown

quit

— graceful shutdown

reload

— reloading the configuration file

reopen

— reopening the log files

For example, to stop nginx processes with waiting for the worker processes to finish serving current requests, the following command can be executed:

nginx -s quit

This command should be executed under the same user that started nginx.

Changes made in the configuration file will not be applied until the command to reload configuration is sent to nginx or it is restarted. To reload configuration, execute:

nginx -s reload

Once the master process receives the signal to reload configuration, it checks the syntax validity of the new configuration file and tries to apply the configuration provided in it. If this is a success, the master process starts new worker processes and sends
messages to old worker processes, requesting them to shut down. Otherwise, the master process rolls back the changes and continues to work with the old configuration. Old worker processes, receiving a command to shut down, stop accepting new connections and
continue to service current requests until all such requests are serviced. After that, the old worker processes exit.

A signal may also be sent to nginx processes with the help of Unix tools such as the

kill

utility. In this case a signal is sent directly to a process with a given process ID. The process ID of the nginx master process is written, by default, to
the

nginx.pid

in the directory

/usr/local/nginx/logs

or

/var/run

. For example, if the master process ID is 1628, to send the QUIT signal resulting in nginx’s graceful shutdown, execute:

kill -s QUIT 1628

For getting the list of all running nginx processes, the

ps

utility may be used, for example, in the following way:

ps -ax | grep nginx

For more information on sending signals to nginx, see Controlling nginx.

Configuration File’s Structure

nginx consists of modules which are controlled by directives specified in the configuration file. Directives are divided into simple directives and block directives. A simple directive consists of the name and parameters separated by spaces and ends with a
semicolon (

;

). A block directive has the same structure as a simple directive, but instead of the semicolon it ends with a set of additional instructions surrounded by braces (

{

and

}

). If a block directive can have other
directives inside braces, it is called a context (examples: events, http,server,
and location).

Directives placed in the configuration file outside of any contexts are considered to be in the main context. The

events

and

http

directives reside in the

main

context,

server

in

http

,
and

location

in

server

.

The rest of a line after the

#

sign is considered a comment.

Serving Static Content

An important web server task is serving out files (such as images or static HTML pages). You will implement an example where, depending on the request, files will be served from different local directories:

/data/www

(which may contain HTML files)
and

/data/images

(containing images). This will require editing of the configuration file and setting up of a server block inside the http block
with two location blocks.

First, create the

/data/www

directory and put an

index.html

file with any text content into it and create the

/data/images

directory and place some images in it.

Next, open the configuration file. The default configuration file already includes several examples of the

server

block, mostly commented out. For now comment out all such blocks and start a new

server

block:

http {
server {
}
}

Generally, the configuration file may include several

server

blocks distinguished by ports on which they listento
and by server names. Once nginx decides which

server

processes a request, it tests the URI specified in the request’s header against the parameters of the

location

directives
defined inside the

server

block.

Add the following

location

block to the

server

block:

location / {
root /data/www;
}

This

location

block specifies the “

/

” prefix compared with the URI from the request. For matching requests, the URI will be added to the path specified in the root directive,
that is, to

/data/www

, to form the path to the requested file on the local file system. If there are several matching

location

blocks nginx selects the one with the longest prefix. The

location

block above provides the
shortest prefix, of length one, and so only if all other

location

blocks fail to provide a match, this block will be used.

Next, add the second

location

block:

location /images/ {
root /data;
}

It will be a match for requests starting with

/images/

(

location /

also matches such requests, but has shorter prefix).

The resulting configuration of the

server

block should look like this:

server {
location / {
root /data/www;
}
location /images/ {
root /data;
}}

This is already a working configuration of a server that listens on the standard port 80 and is accessible on the local machine at

http://localhost/

. In response to requests with URIs starting with

/images/

, the server will send files
from the

/data/images

directory. For example, in response to the

http://localhost/images/example.png

request nginx will send the

/data/images/example.png

file. If such file does not exist, nginx will send a response indicating
the 404 error. Requests with URIs not starting with

/images/

will be mapped onto the

/data/www

directory. For example, in response to the

http://localhost/some/example.html

request nginx will send the

/data/www/some/example.html

file.

To apply the new configuration, start nginx if it is not yet started or send the

reload

signal to the nginx’s master process, by executing:

nginx -s reload

In case something does not work as expected, you may try to find out the reason in

access.log

and

error.log

files in the directory

/usr/local/nginx/logs

or

/var/log/nginx

.

Setting Up a Simple Proxy Server

One of the frequent uses of nginx is setting it up as a proxy server, which means a server that receives requests, passes them to the proxied servers, retrieves responses from them, and sends them to the clients.

We will configure a basic proxy server, which serves requests of images with files from the local directory and sends all other requests to a proxied server. In this example, both servers will be defined on a single nginx instance.

First, define the proxied server by adding one more

server

block to the nginx’s configuration file with the following contents:

server {
listen 8080;
root /data/up1;

location / {
}
}

This will be a simple server that listens on the port 8080 (previously, the

listen

directive has not been specified since the standard port 80 was used) and maps all requests to the

/data/up1

directory on the local file system. Create
this directory and put the

index.html

file into it. Note that the

root

directive is placed in the

server

context. Such

root

directive is used when the

location

block selected for serving a request
does not include own

root

directive.

Next, use the server configuration from the previous section and modify it to make it a proxy server configuration. In the first

location

block, put the proxy_pass directive
with the protocol, name and port of the proxied server specified in the parameter (in our case, it is

http://localhost:8080

):

server {
location / {
proxy_pass http://localhost:8080; }

location /images/ {
root /data;
}}

We will modify the second

location

block, which currently maps requests with the

/images/

prefix to the files under the

/data/images

directory, to make it match the requests of images with typical file extensions. The
modified

location

block looks like this:

location ~ \.(gif|jpg|png)$ {
root /data/images;
}

The parameter is a regular expression matching all URIs ending with

.gif

,

.jpg

, or

.png

. A regular expression should be preceded with

~

. The corresponding requests will be mapped to the

/data/images

directory.

When nginx selects a

location

block to serve a request it first checks location directives that specify prefixes, remembering

location

with
the longest prefix, and then checks regular expressions. If there is a match with a regular expression, nginx picks this

location

or, otherwise, it picks the one remembered earlier.

The resulting configuration of a proxy server will look like this:

server {
location / {
proxy_pass http://localhost:8080/; }

location ~ \.(gif|jpg|png)$ {
root /data/images;
}}

This server will filter requests ending with

.gif

,

.jpg

, or

.png

and map them to the

/data/images

directory (by adding URI to the

root

directive’s parameter) and pass all other requests to the
proxied server configured above.

To apply new configuration, send the

reload

signal to nginx as described in the previous sections.

There are many more directives that may be used to further configure a proxy connection.

Setting Up FastCGI Proxying

nginx can be used to route requests to FastCGI servers which run applications built with various frameworks and programming languages such as PHP.

The most basic nginx configuration to work with a FastCGI server includes using the fastcgi_pass directive instead of the

proxy_pass

directive,
and fastcgi_param directives to set parameters passed to a FastCGI server. Suppose the FastCGI server is accessible on

localhost:9000

. Taking
the proxy configuration from the previous section as a basis, replace the

proxy_pass

directive with the

fastcgi_pass

directive and change the parameter to

localhost:9000

. In PHP, the

SCRIPT_FILENAME

parameter
is used for determining the script name, and the

QUERY_STRING

parameter is used to pass request parameters. The resulting configuration would be:

server {
location / {
fastcgi_pass  localhost:9000;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
fastcgi_param QUERY_STRING    $query_string;
}

location ~ \.(gif|jpg|png)$ {
root /data/images;
}}

This will set up a server that will route all requests except for requests for static images to the proxied server operating on

localhost:9000

through the FastCGI protocol.